Xanthate dissolver



Feb. 2, 1960 H. FAWLEY EI'AL 2,923,604

XANTHATE DISSOLVER 2 Sheets-Sheet 1 Original Filed Aug. 13, 1954 O 000 0000 u 0 0 0 0 0nd! Feb. 2, 1960 H. FAWLEY ETAL 2,923,604

XANTHATE DISSOLVER Original Filed Aug. 13, 1954 2 Sheets-Sheet 2 XANTHATE DISSQLVER 7 Harry Fawley, Lewistowmlvii chael *Golben, Ridley Park, "and David J. Dub, Bnrnham, Pa., assignors to Amencan Viscose Corporation, Philadelphia, Pa., 2 corporation of Delaware Original application August 13, 1954, Serial No. 449,598. 0

Divided and this application February 18, 1957,'Serial 4 Claims. (11. 23-1236) fairly conventional. In general, the cellulose (cotton linters, purified wood pulp, or the like) is impregnated (steeped) with concentrated aqueous sodium hydroxide to form alkali cellulose, the excess caustic soda solution squeezed out, the pressed cake shredded into crumbs, the crumbs aged undercontrolled conditions (time, temperature, exposure to oxygen, etc.) to degrade the cellu lo se for proper viscose viscosity, the aged crumbs treated with carbon .bisulfide to produce cellulose xanthate (a' lumpy orangecolored product varying from a mealy to a sticky consistency), the xanthate dissolved or dispersed in dilute aqueous caustic alkali, the solution or dispersion filtered and the resultant viscose ripened (aged) until suitable for extrusion and regeneration into filaments, films, tubes and the like.

Due to the nature of the cellulose xanthate, i.e., its stickiness and tendency to form relatively large balls'or' crumbs, it has been a particularly difiicult problem to dissolve the cellulose xanthate in an alkaline solution. Another difficulty encountered in dissolving the xanthate is the presence in the xanthate crumbs of alkali-insoluble cellulosic particles, e.g., coated fibers, fiber gel and gels aswell as extraneous matter that may be picked up in the. viscose making'process. These cellulosic particles are microscopic in size with diameters ranging from submicroscopic to 100 microns as distinguished from the visible microscopic crumbs composed of bundles of alkalisoluble xanthated alkali cellulose fibers. In the prior art methods of dissolving, there has been no differentiation as to work done onthe dissolved viscose, insoluble cellulosic particles and xanthate crumbs.

It has been discovered that the energy expended in performingattrition on completely dissolved xanthate and the insoluble cellulose particles is not only unnecesary, but that the resulting comminution of the insoluble particles permits their passage through the course filter media into the fine filter material where the passageways are easily clogged, and increases the probability that some of the shredded gels andfiber gels will pass all filters and contribute to poor quality in thefinal viscose.

The'present invention, therefore, contemplates, and

Patented Feb. 2,

Unexpectedly,'in additionto considerable savings in energy,*the viscose solution produced by the method of this invention can be filtered with less frequent changes in the filtering media and with fewer undissolved particle in the filtered viscose.

Referring now to the drawings:

Fig. 1 is a view partially in section and partially inside elevation of one form of apparatus according to the present invention;

Figf 2 is a sectional view taken along the line I III of Fig; 1; t

Fig; 2a is a sectional view taken along the line Ila-Ila of Fig. l;

Fig. 3 is a diagrammatic view of a modified 'form of apparatus;

Fig. "4 is a diagrammatic view of another modification; and

FigflS' illustratesthe determination described hereinbelow of the size and shape of agiven xanthate crumb that will readily dissolve without further comminution.

The apparatus shown in Figs. 1 and 2 is described in detail as follows: means for xanthating aged alklali cellulose such as hexagonal churn 5 is provided. A funnel 6 to direct the xanth'ate into vessel 7 through inlet port;

8 may be'employed. t

Within vessel 7 is rotatably mounted an open-ended cylindrical perforated screen 9 fixed, as best shown in Fig. 2a, by means ofspokes 11a to a sleeve 10 which is rotatably mounted in the top portion'of vessel 7 and drivenbya motor 12 through a gear box 13. An independently rotatable shaft 22 extends through the sleeve 10 and has a bearing at its lower end within a non-rotatable sleeve bearing 10a and spokes 11 extending inwardly from the cylindrical'screen 9 are securedat their inner ends to sleeves which loosely surround the shaft 22. "The spokes 11 thus provide lateral support for the screen9. V t

A bracket 16 loosely mounted on the sleeve 10 and a bracket 17 secured to the bearing sleeve 10a supports shaftsml5 on which are rotatably-mounted smoothsurfaced squeeze rollers 14. A ring gear 18 is secured to" the upper end of screen. 2 andmeshes with pinions 19 secured to the squeeze rollers 14 so that as the screen .9 rotates the rollers 14 are rotated in the opposite direction. The axes of rollers 14 are parallel of the axis of cylindrical screen 9 and the surfaces of rollers 14 contact the outside surface of screen 9 along substantially straight lines at any given rotational position so as to provide a nip between the rollers 14 and the screen 9 as on shaft 22 near the opposite ends of screen 9. Valve 25 is an inlet for alkalinesolutions. JThermometer 26 measures the temperature within the vessel 7. Outlet 27 is provided for dischargingthe viscose-solution. Vessel 7 is circumscribed by a jacket .28 which allows cooling fluid to be circulated between the exterior of vessel 7 and jacket 28 as shown. t t

In operation, the above described apparatus is charged with both cellulose xanthate crumbs and alkaline solution sufiicient to prepare a viscose with predetermined cellulose content, caustic content, etc. Rotation is imparted to both sleeve 10 and shaft 22 causing the perforated screencylinder 9 to rotate in an opposite dircction'to the rollers 14 thereby affording means for forcing xant hate crumbs larger than the perforations in cylinder 9 through the perforations and thus comminute or alter the shape of the crumbs so that no point in the mass of any given crumb will be greater than the penetration of the alkaline tion thus acts as a medium for directing the oversize crumbs into the nip of screen 9 and rollers 14. As rotation of both sleeve 10 and shaft 22 continues, substantially allot the xanthate crumbs tend to pass through the perforations in cylinder 9 without being forced, by the rollers 14, and, therefore, rotation of sleeve 10 may be discontinued after sufficient comminution of the crumb and cir,-

oulation of the xanthate-alkaline solution -mixture by screws and 21 continued until the xanthate crumbs are nolonger visible. The viscofse solution is then discharged, filtered, aged, and extruded to form fibers or film.

Referring to Fig. 3, the alternative of comminution the relatively large crumbs prior to mixing with the alkaline solution is described as follows: crumbs which are. discharged from xanthater 29 pass through screen 3.0 into mixing tank 34 through funnel 35 as the size and shape admits ready penetration by the. alkaline solution. The oversized crumbs are forced through screen 30 by the motion of the rolls 31 mounted to rotatable shaft 3-2 which is driven by motor 33. All of the xanthate crumbs therefore are of an acceptable size for efficient dissolution in tank 34 with the aid of a suitable agitating means such as rotary stirrer 36. .2

. Fig. 4 illustrates the other alternative of first forming a concentrated slurry oftthe xanthate crumbs andless than the amount of alkaline solution to be finally mixedrwith the xanthate. The slurry is comminuted invessel 7? having essentially the same structure within as vessel..7 :in Fig. 1. The slurry of comminuted xanthate crumbs and alkaline solution is then transferred to tank 34', similar to tank 34, where the remaining quantity of alkaline solution is added and the mixture agitated by stirrer 365, similar to stirrer 36, until xanthate crumbs are nov longer visible to the naked eye. 11

In each of the above alternatives described, there is substantially no disintegration of the microscopicinsoluble particles and the comminuting or shaping effect .is generally limited to the relatively large xanthate crumbs.

To determine the maximum size of cellulose xanthate crumbjwhich can be readily penetrated by the alkaline solution those skilled in the art can check the ease of Fig.- 5; and, therefore, its radius, r, must beless thantheabove set forth maximum distance for any given point from a point on the surface of the crumb. 4

The-viscose produced by the method of this invention has improved filterability and is freer from insoluble matter after filtration than a viscose produced by the-- attrition methods that are taught by. the. prior art. Filterability is defined as the average rate of change of filter pressure with respect to time, i.e., as the viscose solution is forced through a standard candle filter at a constant rate for a given period of time, the pressure required to force the viscose through the filter increases and the average rate of increase over a period of 6 hours is determined. Filterability determined by this method is termed herein the T value. Filterability may also be determined by the standard plugging factor test.

Examplesl and 2 illustrate prior art methods and the remaining examples illustrate this invention. and represent preferred embodiments thereof. The T values given forv the viscose produced in each example was determined in the same manner so as to give results which indicate the filterability between each viscose solution, a lower value indicating a better filterability.

Example 1 25 pounds of a rayon-sulphite-spruce pulp (alpha cellulose content 88.5% polymerization degree 800) were steeped in an 18% NaOH solution and the excessive lye pressed off. This alkali cellulose was shredded, aged 17 hours at 34 C. and xanthated with an excess of CS in a conventional xanthate churn. 8.5 pounds of the resulting Example 2 25 pounds of the same type of sulphite pulp asus'ed in Example 1 were converted into cellulose xanthate 'c'rumbs in accordance with the method of Example 1,. 8.5 pounds of the xanthate crumb was mixed with 3 gallons of 14% NaQH solution in a conventional xanthate dissolving vesselwhe'rein the mixture was subject to the disintegrating action of high speed shearing type blades. After three hours a homogeneous solution appeared to have been produced'with the same cellulose content and viscosity as the viscose produced in Example 1. The T value was 14: m

3 Example 3' r e 8.5 pounds of cellulose xanthate crumbs were preparedfrom the same pulp and in the same manneras in Example I and the crumbs varied in size from about ,1 of an. inch in diameter to inch in diameter. These crumbs were passed over a screen having holes 4inch in diameter. screen were forced through by a roller into a vessel containing the A1. inch or smaller crumb. Three gallons of 12% .NaOH solution was added to thevessel and-the mixture agitated with a conventional three blade propeller type stirrer. Cooling water was circulated in a jacket surrounding the vessel maintaining thetemperature within the vessel at 17.5" C. during dissolution. The. xanthate crumbs disappeared from sight in 2.5 hours. The resulting viscose hada viscosity of 32 second's, a cellulose content of 8.1%, and a yalue of 7.

Example 4 8.5 pounds of cellulose xanthate crumb was prepared in 'the'same manner as Example I but the starting materialzwas cotton liuters instead of woodpulp. Crumbs which did not pass through a inch screen .Were forced through and the entire batch of crumb charged'into the.

same'vessel as Example 3 and 3 /2 gallons of 12% NaOH solution added. The mixture was stirred in the. same vmanner as Example 3 and the temperature kept constant at 717.5" C. during the dissolution. The lastcrumb dis-. appeared from sight after 1.75 hours of mixing.- 1 The Y content of 8.7% and a T value of 7. 5

" v v Example 5 resulting viscose had a viscosity of 39 seconds, a cellulose of cellulose xanthate crumbsfromfi-to l inch-in diameter were prepared from the same materials and in the same manner as Example I. The crumbs were charged intoa'vessel together withthree gallons of 14% crumbs comminuted by the apparatus shown'in Figure 1,

Crumbs which did not pass throughthe I the symmetrical revolving screen 9 having holes A inch in diameter. The last crumbs disappeared in two hours. The temperature during dissolution was kept constant at 175 C. The resulting viscose had a viscosity of 36 seconds, a cellulosic content of 8.3% and a T value of 8.

Example 6 14 pounds of cellulose xanthate crumbs were prepared from purified sulphite-spruce pulp in accordance with the method set forth in Example I. The diameters of the crumbs ranged from inch to inch and were placed in the same vessel as described in Example 5. 2.5 galions of 14% NaOH solution was added and the comrninution of the larger xanthate crumbs effected as in Example 5. After /2 hour mixing in this vessel, the slurry was charged into another vessel. The slurry mixing vessel was rinsed with two gallons of 14% NaOH solution and this solution added to the slurry in the other vessel. The mixture of the slurry and NaOH solution was agitated for 1.75 hours by a three blade propeller type stirrer driven at 1725 r.p.m. by a A horsepower electric motor, a homogeneous viscose resulting with a viscosity of 37 seconds, a cellulose content of 8.2% and a T value of 7.

It is to be understood that the aforegoing examples and description are merely illustrative and that changes and modifications may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.

We claim:

1. An apparatus for dissolving cellulose xanthate crumbs in an alkaline solution comprising a closed vessel, means for admitting cellulose xanthate crumbs and an alkaline solution into said vessel, an open-ended, perforated, hollow cylindrical member rotatably mounted within said vessel, means for rotating said member about the longitudinal axis thereof, a roller mounted within said vessel on an axis parallel to the axis of said cylindrical member, the surface of said roller being in contact with a surface of said cylindrical member, means for rotating said roller in the direction opposite to the rotation of said cylindrical member whereby the cellulose xanthate crumbs will be caught between the roller and the cylindrical member and forced through the perforations in the latter, and means for circulating the mixture of crumbs and alkaline solution through the perforations of said cylindrical member and the open ends thereof.

2. The apparatus of claim 1 wherein the roller is 1ocated outside said cylindrical member.

3. The apparatus of claim 1 wherein a driven shaft extends through said cylindrical member along the longitudinal axis thereof and the means for circulating the mixture comprises oppositely pitched screws mounted on said shaft.

4. The apparatus of claim 3 wherein the roller is located outside said cylindrical member and the mixture is circulated through the perforations of said cylindrical member from the outside to the inside thereof and from the inside back to the outside through the open ends of said member.

References Cited in the file of this patent UNITED STATES PATENTS 2,614,102 Schlosser et al Oct. 14, 1952 

1. AN APPARATUS FOR DISSOLVING CELLULOSE XANTHATE CRUMBS IN AN ALKALINE SOLUTION COMPRISING A CVLOSED VESSEL, MEANS FOR ADMITTING CELLULOSE XANTHATE CRUMBS AND AN ALKALINE SOLUTION INTO SAID VESSEL, AN OPEN-ENDED, PERFORATED, HOLLOW CYLINDRICAL MEMBER ROTATABLY MOUNTED WITHIN SAID VESSEL, MEANS FOR ROTATING SAID MEMBER ABOUT THE LONGITUDINAL AXIS THEREOF, A ROLLER MOUNTED WITHIN SAID VESSEL ON AN AXIS PARALLEL TO THE AXIS OF SAID CYLINDRICAL MEMBER, THE SURFACE OF SAID ROLLER BEING IN CONTACT WITH A SURFACE OF SAID CYLINDRICAL MEMBER, MEANS FOR ROTATING SAID ROLLER IN THE DIRECTION OPPOSITE TO THE ROTATION OF SAID CYLINDRICAL MEMBER WHEREBY THE CELLULOSE XANTHATE CRUMBS WILL BE CAUGHT BETWEEN THE ROLLER AND THE CYLINDRI- 